This can be managed by looking at the "Days left" and "Reorder due date" fields in StockTrim, and setting the lead time accordingly.
But generally, from an order planning perspective, the timing of the delivery of on-order amounts is only relevant when planning the orders, and not relevant after they have been placed, because if managed correctly they should have always been placed in the past with enough time in advance (the lead time) so they arrive at the time they are needed to meet demand.
StockTrim will always suggest the order quantity to cover your expected demand between now and the lead time (when they are due to arrive). So even if you are in a situation where you're currently expected to run out of stock (for example if you have a lead time of 6 months, but only 4 months of stock on hand), if you place the required orders to cover 6 months now, and repeatedly order every 2 - 4 weeks the suggested quantities to cover the next 6 months at each point in time, your stock will eventually balance out.
So after using StockTrim for several months, and following the suggestions, you should end up in a scenario where the current stock on order is arriving at the exact date it is required.